Retransmission-Based Access Class Barring for Machine Type Communications

Supporting trillions of devices is the critical challenge in machine type communication (MTC) communications, which results in severe congestions in random access channels of infrastructure-based cellular systems. 3GPP thus developed the access class barring (ACB) to control the expected number of simultaneous access requests in a preamble as one. The assignment of classes with specific access parameters for MTC devices becomes an cirtical issue in ACB since it affects the performance from the perspectives of successful access probability and access delay significantly. This paper proposes a novel classification scheme where we group MTC devices according to their number of transmission trials while without introducing extra overheads. A heuristic algorithm is proposed, where the devices with more number of retransmission failures will have more chance to access the preamble. By adaptively changing the ACB factor, the proposed heuristic algorithm can reduce the access delay effectively while maintaining high access success probability. The simulation results show the improvement of the proposed scheme from the existing ACB schemes.